auxetic polymers for medical device technology
TRANSCRIPT
Auxetic polymers for medical device technology
“Medical and stretchy”
Andy Alderson
Professor of Smart Materials and Structures
Director Industry & Innovation Research Institute
+44 114 225 3523
http://www.linkedin.com/pub/andrew-
alderson/15/123/625
Auxetic Materials
Naturally-occurring auxetic materials
Biomaterialso Cat skino Cow teat skino Carotid arterieso Achilles tendono Stem cell nucleio Amphibian embryo
tissueo Annulus fibrosus
(Chen & Brodland, Journal of the
Mechanical Behaviour of Biomedical
Materials 2 (2009) 494-501)
Minerals & polymerso a-quartzo a-cristobaliteo Mother-of-pearlo Zeoliteso Talco Cellulose
Auxetic cat skin
Veronda & Westmann, J. Biomechanics (1970)
Cat skin
Frohlich et al, J. Zool. Lond. (1994)
Veronda & Westmann, J. Biomechanics (1970)
In-plane
Thru’
thickness
Poisson’s ratio:xy = -(y/x)
Auxetic Material: Material with a negative Poisson’s ratio
+ve xy
-ve xy
Auxetics: a route to
enhancing other properties
G = Shear modulus
Maintains shape
Maintains volume
K = Bulk modulus
12
213
K
G
For isotropic materials: -1 < < +0.5
212
r
ET
12
213
K
G
Auxetics: a route to
enhancing other properties
Shear rigidity
Fracture toughness
For isotropic materials:
-1 < < +0.5
For isotropic materials: -1 < < +0.5
212
r
ET
12
213
K
G
Auxetics: a route to
enhancing other properties
3/2
21
EH
Shear rigidity
Indentation
resistance
Fracture toughness
For isotropic materials:
-1 < < +0.5
For isotropic materials: -1 < < +0.5
E
U v6
21 2
212
r
ET
12
213
K
G
Auxetics: a route to
enhancing other properties
3/2
21
EH
Shear rigidity
Indentation
resistance
Fracture toughness
Volumetric strain
energy dissipation
For isotropic materials:
-1 < < +0.5
For isotropic materials: -1 < < +0.5
E
U v6
21 2
212
r
ET
12
213
K
G
Auxetics: a route to
enhancing other properties
3/2
21
EH
Shear rigidity
Indentation
resistance
Fracture toughness
Volumetric strain
energy dissipation
Critical resonance
frequency
For isotropic materials:
-1 < < +0.5
𝑓𝑐 ∝ 1 − 𝜈2 Τ1 2
For isotropic materials: -1 < < +0.5
Ability to naturally adopt dome
shape when bent out of plane
E
U v6
21 2
212
r
ET
Curvature
Non-auxetic Auxetic
12
12
RR
12
213
K
G
Auxetics: a route to
enhancing other properties
3/2
21
EH
Shear rigidity
Indentation
resistance
Fracture toughness
Volumetric strain
energy dissipation
𝑓𝑐 ∝ 1 − 𝜈2 Τ1 2 Critical resonance
frequency
For isotropic materials:
-1 < < +0.5
For isotropic materials: -1 < < +0.5
https://www.d3o.com/wp-content/uploads/2016/09/D3O-TRUST-Helmet-pad-system.pdf
https://wavecel.trekbikes.com/us/en_US/
WaveCel - Bontrager
Under Armour 3D-printed sports shoesUA Architech - latticed upper made from Clutchfit Auxetic materials
https://www.youtube.com/watch?v=3fH9UVEfLyo
Nike Womens Free Run Flyknithttps://www.youtube.com/watch?v=3M5jEB4-H0M
PUMA Calibrate Runnerhttps://www.youtube.com/watch?v=K8pa
hZAmAV0&feature=youtu.be
Am I in the right place?
The Poisson’s ratio () scale
0 +0.5-1
Cork
‘Typical’ materials
Rubber
a-cristobalite
Crystalline cellulose
Microporous polymers
Annulus fibrosus
Auxetic or ‘anti-rubber’ materials
Annulus fibrosus
Auxetic elastomer developments
• Auxetic fabrics containing elastomeric fibres
• Auxetic fibre-reinforced elastomer composites
• Auxetic Liquid Crystal Elastomers
• Made on commercial warp knitting
machine
• Commercially-available,
conventional yarns
– 480dtex Dorlastan V500
– Polyester monofilament of 0.15 and
0.25mm diameters
• Apparel applications
– Comfort, fit, breathable garments
• Healthcare applications
– Breathable wound-healing
bandages
Sara Lee Branded Apparel/Hanes
Brands Inc/Global Composites
Group
PCT Patent Publication Nos.
WO2008/016690; WO2010/125397
Fabrics:Auxetic fabric structure
WARP KNIT STRUCTURES BASED ON TRIANGULAR
LATTICE GEOMETRY
WARP KNIT STRUCTURES BASED ON TRIANGULAR
LATTICE GEOMETRY
•Negative in-plane or out-of-plane Poisson’s ratios possible
for certain lay-up sequences
Auxetic composites:Angle-ply laminates
CLT predictions for in-plane Poisson’s ratio
xy as a function of angle q for various fixed
angle a values in an unbalanced
graphite/polyurethane laminate with a lay-up
of [q/a]s
L. D. Peel, Phys. Stat. Sol. B 244(3) (2007) 988
CLT predictions vs experiment as a function
of angle q for unbalanced [θ2/302]s and
balanced angle-ply [±θ/±30]sgraphite/polyurethane laminates
Auxetic fibre-reinforced elastomer composites
Auxetic Liquid Crystal Elastomers
Crystalline cellulose – Kraft cooked spruce
Experimental data
Tc [min]
Poisson’s ratios
31
(before yield)
31
(after yield)
120 -1.06±0.53 -0.98±0.46
150 -0.91±0.25 -1.00±0.25
180 -0.76±0.3 -0.86±0.25
210 -1.17±0.26 -1.05±0.26
240 -0.26±0.15 N/A
M. Peura, et al (2006),
Biomacromolecules, 7, 1521-1528
x3
x1
x3
x2
• 3 (3) > 0
• 1 > 0 → 31 < 0
• 2 < 0 → 32 > 0
Applying the cellulose chain model to
mesogen rotation in auxetic LCEs
Shruti Mandhani
MPG / RIEG Webinar - Elastomers and Polymers - Can the demand for improved sustainability be satisfied?16th November 2020
MERI-BMRC-SCH collaboration:Auxetic scaffolds for tissue engineering
Cell growth & proliferation #11yr u/g placement
student: Jordan RoeSupervisors:
C. Le Maitre (BMRC), AA, N. Jordan-Mahy
(BMRC) & P. Godbole(SCH)
2015-2016
Cell growth & proliferation #2
1yr RA: Paul MardlingSupervisors:
C. Le Maitre (BMRC), AA, N. Jordan-Mahy
(BMRC) & P. Godbole(SCH)2017
Tissue Engineering
VCS PhD student: Paul MardlingSupervisors:
C. Le Maitre (BMRC), AA, N. Jordan-Mahy
(BMRC)Advisor: P. Godbole
(SCH)2018-2021
Why auxetic scaffolds?
• Increasing number of natural soft biological tissues reported to display auxetic behaviour
• Preliminary report (Park 2013) that auxetic PU foam scaffold under compression leads to enhanced physical stimulation for cellular proliferation during cell cultivationo 1.3 times higher cellular proliferation rate 3 days after cell
seeding
o 1.5 times higher amount of collagen produced by the cells after 3
and 5 days in culture
PhD: Investigating the Use of Auxetic
Materials Within Tissue Engineering
Aim/Objectives Methodology
Create auxetic scaffolds Thermomechanical triaxial compression
Assessment of mechanical properties 3D Digital image correlation
Culture human cells within auxetic scaffolds Various primary cell types seeded within auxetic scaffolds and cultured for up to 4 weeks.
Assessment of cell culture Histology:• Haematoxylin and Eosin : Cell morphology• Masson’s trichrome : Extracellular matrix• Immunohistochemistry: Cell markers
Culture human cells within auxetic scaffolds under physiological load
Using a bioreactor to grow cell seeded scaffolds under cyclic physiological load.
Assessment of cell culture Histology:• Haematoxylin and Eosin : Cell morphology• Masson’s trichrome : Extracellular matrix• Immunhistochemistry: Cell markers
Key results and outcomes/conclusions to date
• Development of auxetic scaffolds successful– Another novel scaffold currently in development
• Cell culture of seeded scaffolds for 4 weeks– Cells attach– Proliferate– Currently checking differentiation status
• Cell culture under cyclic physiological load– ongoing
SEM & Histology comparison
3D DIC Tissue samples
Composite Foam-
Hydrogel Scaffold
Converted
• xxxxx
Converted containing Hydrogel
Com
posite S
caffold
Storage and release of guest material:High volume change (variable porosity membranes)
Movie courtesy of BNFL (source: BNFL ‘World Beating Science’ CD-ROM)
Strain in loading direction
0.000 0.004 0.008 0.012
n/n 0
0.5
0.6
0.7
0.8
0.9
1.0
1.1
x ;
xy= -1.4
y ;
yx= -0.18
No.
blo
cked p
ore
s
‘SMART’ BANDAGE: IMPREGNATED AUXETIC FILAMENTS
Bandage applied
to wound
• bandage consists of
auxetic filaments
impregnated with
wound-healing agent
Infected
wound swells
• bandage stretches
• filaments stretch
• filament micropores open
(auxetic effect)
• release of wound-healing
agent starts
Wound heals
• swelling decreases
• bandage relaxes
• filaments relax
• filament micropores close
• release of wound-healing
agent stops
A.Alderson, Presentation to Engineering Council 2001
A.Alderson, K.L.Alderson, Technical Textiles International, 14(6) (2005) 29.
Healthcare case study: the LaparOsphereTM
• 3 million abdominal laparoscopic (key-hole) procedures are undertaken each year
• Expect increasing use of laparoscopic techniques to reduce patient trauma, speed up operations and reduce healthcare costs
• CO2 insufflation currently used to visualise the area of interest and create a space to operate within. Issues include:
– Raised abdominal pressure can result in reduced heart and lung function, hypercapnia and hypoxaemia
– CO2 losses due to the use of suction devices and leakage
– Difficulties in using electrosurgical and laser based cutting and sealing devices
– Requirement for additional and frequent organ retraction
LaparOsphereTM
Innovative new device for space creation and organ retraction in laparoscopic surgery
(Dr James Corden (TrusTECH), “Auxetic Technology in Improving Healthcare”,
Materials KTN workshop, 4th September 2012)
Potential to contribute to cost savings, reduced lengths of stay, reduced complications
and reduced adverse events associated with laparoscopic procedures
• Provides improved access and visibility for the surgeon
• Eliminates patient side effects associated with CO2 insufflation
• Enables use of suction without deflation
• Improved use of thermal cutting systems
• No need for multiple gas tight access ports
• Eliminates recurrent deflation caused by CO2
leaks
• No requirement for medical grade CO2
• With its innate retraction function on inflation, reduces need for additional instruments
Deployable auxetic cylinders
PhD student: Dignesh Shah
Sector case study: Healthcare
Auxetic foam pads will improve wearer
acceptance and compliance in hip protector
devices due to:
• improved comfort/fit (double curvature)
• enhanced energy absorption (impact
response)
• lower device weight and/or volume
Hip implants with auxetic mesh stems
provide
• improved match to bone mechanical
properties
• reduced ‘stress shielding’
• a compensation mechanism for
loosening of the stem over time -
extending device lifetime and time
between implant replacement operations
Deployable gradient
auxetic structures for
space creation and
organ retraction in
keyhole surgery
The 'smart bandage' concept delivers controlled drug release
from wound dressings in response to swelling of the wound
Gradient one-piece foams
mimic the concentric core-
sheath structure of the
natural intervertebral disc.
The auxetic sheath
reduces disc bulge under
compression to reduce
lower back pain